The present invention relates to removal of sulfuric acid in a combustion exhaust gas which is required in a carbon dioxide capture power generation system.
Recently, global warming is attracting attention as a global environmental issue. It has become clear that the increase of carbon dioxide concentration in the atmosphere is the main factor of the global warming, and reduction of carbon dioxide emission has become important.
Coal thermal power stations are dominant emission sources of carbon dioxide, and high-efficiency separation and capture of the carbon dioxide in the combustion exhaust gas have become a subject to be challenged.
In the conventional coal thermal power generation, fuel is combusted using air, and the air contains an about 80% of nitrogen which is not involved in the combustion, and this nitrogen has been a disincentive for the high-efficiency separation and capture of carbon dioxide.
In order to remove this disincentive, JP-3068888, for example describes a method in which coal is combusted with oxygen. By combusting with oxygen which contains no nitrogen, the concentration of the carbon dioxide in the combustion exhaust gas can be increased so as to allow the high-efficient separation and capture of carbon dioxide.
On the other hand, since the temperature of the combustion exhaust gas becomes high in the combustion with oxygen, in order to prevent boiler materials from becoming intolerable against the temperature, a part of the combustion exhaust gas is recycled to the boiler to decrease oxygen concentration, and thereby the temperature of the combustion exhaust gas is maintained at a level similar to the case of the combustion with air.
Since when coal is combusted in a boiler, nitrogen oxides (hereinafter, referred to as NOx) and sulfur oxides (hereinafter, referred to as SOx) are generated, equipments to purify these oxides are installed in the wake flow of the boiler. The NOx is converted to nitrogen by being reacted with ammonia using a denitration catalyst. The SOx is reacted with caustic lime to form gypsum. In addition, a part of the SOx becomes a sulfuric acid gas. When the temperature of the combustion exhaust gas becomes the sulfuric acid dew point or lower, the acid liquefies and generates sulfuric acid mist. This sulfuric acid mist adheres to members of the equipment and pipings to cause corrosion of the members. Further, the sulfuric acid mist generates white smoke when discharged through a stack, causing visual pollution. Furthermore, the sulfuric acid mist becomes a source of acid rain. Due to these reasons, an equipment to remove sulfuric acid in the combustion exhaust gas is installed.
Method to remove sulfuric acid mist includes, for example, a method of JP-A-2002-45643 is described, in which a wet electrostatic precipitator is provided in the wake flow of a desulfurization equipment to make the sulfuric acid mist charged to remove it and the sulfuric acid mist is coarsened to improve the removal performance.